Cutting inserts are typically used for chip removing metal cutting operations, such as turning, milling or drilling operations. In many cases, a cemented carbide shim is interposed between the cutting insert and a bottom wall of a tool holder pocket. The shim is then serving to protect the tool holder pocket from excessive wear or damage through use. Embossing of the cutting insert into the tool surface is one of the prevented wear mechanisms. In some cases where shims are employed together with screw fastened cutting inserts, the shim is retained in position in the pocket by means of a special screw arranged with an internal screw threading. The special screw fastens the shim to the tool body while the internal screw threading is adapted for the fastening of the cutting insert. The screw used to secure the cutting insert is arranged to pass through the bore of the cutting insert and to engage with the internal threading of the special screw. The shims are typically designed to be directly secured to the bottom wall of the tool holder. The cutting insert facing surface of the shim provides support for the bottom side of the cutting insert.
The cutting inserts are typically manufactured from a particularly hard and wear-resistant material, such as sintered cemented carbide, ceramics, etc. The tool holder body is typically manufactured from a more elastic material, in particular steel. To protect the tool holder pocket from excessive wear or damage, the shim is usually manufactured from a wear-resistant material with high hardness such as cemented carbide. The shim is typically face grinded to a flat and plane-parallel geometry.
The presence of the screw aperture in the shim decreases its largest possible supporting contact area with the cutting insert, and the larger the screw opening the less the possible area of contact between the shim and the cutting insert. There is a demand for smaller and smaller cutting inserts for production of minimal, narrow and advanced products. The holding of small cutting inserts with shims in a tool body is a problem due to the reduced area of contact between the shim and the cutting insert and there is a constant need of rigid fastening arrangements during cutting operations.
Stable and rigid holding of cutting inserts is a crucial issue to reduce the risk of rupture or breakage of the cutting insert. The precision of the holding is of great importance in the cutting operations and is necessary in the production of a final product with small tolerances.